1. Field of the Invention
The present invention relates to a continuously insulated building wall assembly suitable for use in commercial buildings and a method for assembling such wall assembly.
2. Description of Related Art
Commercial buildings in North America are regulated by numerous building codes. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standard 90.1-2007 prescribes thermal insulation requirements, which can require continuous insulation as part of a wall structure. National Fire Protection Association (NFPA) standard 285 identifies flame propagation requirements for exterior non-load bearing wall assemblies. American Society for Testing and Materials (ASTM) standard E-331 dictates water barrier property requirements. ASTM E-2357 dictates air barrier property requirements. In addition to code requirements, designers and builders demand that the building materials be durable enough to withstand at least six months of exposure to elements of weather in any season and rough job site handling without damage or deterioration. In order to meet the stringent demands, commercial buildings often comprise wall systems containing a support framework (for example, a network of studs) with multiple building components on and within the support framework.
Use of exterior grade gypsum board as a substrate over an outer surface of structural members such as studs is common in the industry to create wall structures that meet these stringent building codes. For example, exterior insulation finish systems (EIFS) are one type of common wall system for use in building structures. EIFS use an exterior grade gypsum board as a substrate over structural members such as wall studs. Insulating foam applied over the gypsum board provides thermal insulation. Tape or fillers typically seal seams between gypsum boards and/or insulating foam boards. The EIFS can also include a water barrier membrane to improve water barrier properties (see, for example U.S. Pat. No. 5,027,572 which teaches use of a polyethylene film between the gypsum board layer and thermal insulation layer). Such a wall system suffers from numerous drawbacks. Gypsum board is dense, heavy material that makes installation of the wall system labor-intensive and cumbersome. The wall system requires numerous layers of materials (cavity insulation, gypsum board, water barrier, seam sealing and a thermal insulating barrier) in order to achieve the demanding building code requirements, which in turn require extensive time for installation. Materials such as gypsum board can also suffer from deterioration if moisture penetrates into the gypsum board, a not-unlikely problem in humid or rainy environments.
Wall systems further typically include a water vapor barrier material adjacent to either the inside surface or outside surface of the structural members as well as fiber batting insulation within cavities between structural support members. The water vapor barrier material serves to hinder penetration of moisture into a cavity space between structural support members. Moisture can be particularly problematic in the cavity space when a surface in the cavity space is at a temperature below the dew point of the humidity in the cavity, which results in condensation of the moisture on the cold surface. Fiber batting insulation tends to exacerbate trapping moisture within the cavity spacing between structural members by: (1) insulating the cold surface within the cavity from warmth from the warmer surfaces thereby allowing the cold surface to get colder and induce more condensation than had the insulation not been present; and (2) dramatically increasing the path through which moisture must travel through the cavity space to escape from the cavity space.
A wall assembly that meets the necessary commercial building codes but that does not require gypsum board, or similarly heavy-weight substrate, on the outer surface of the structural members is desirable. Even more desirable is a wall assembly that includes a substrate that is lighter-weight than either gypsum or wood based substrates and that inherently provides a continuous thermal insulating layer to meet ASHRAE 90.1-2007 requirements without requiring both a substrate layer and a thermally insulating layer. Moreover, such a wall assembly would be even more desirable if it would not suffer from deterioration in humid or moist environments. Yet more desirable would be a wall assembly with any combination of these features that is also durable to handling on a job site and open exposure on a building structure for extended periods of time. Yet even more desirable is a wall assembly that inhibits moisture condensation within a cavity spacing between structural members by inhibiting any surface within the cavity spacing from becoming cool enough to reach the dew point for the cavity spacing. Preferably, it would be desirable to have a wall system that does not require a water vapor barrier material to preclude condensation of moisture within a cavity space between structural members. Moreover, it would be desirable to have a wall system that does not require fiber batting in a cavity spacing between structural members in order to achieve desirable thermal insulating properties.